Due to the strong internal stress, the molecules of the tempered glass are firmly bound together, which makes the glass fragile before it becomes more rigid and tougher, and it is not easily broken or crushed.
Because of the huge stress inside the glass, the entire glass, especially at the corners, is always in a tight state. Even if there is a little scratch or damage on its surface, the stress will be concentrated on this point, breaking the original balance from the surface, causing the molecular bond to be broken at the break. The energy for molecular bond breakage is transmitted inside the glass at the speed of sound, and the stress accumulated in the glass will be released from the weakest place nearby, thus causing extensive molecular bond breakage.
Therefore, when extensive molecular bond breaks are caused, the tempered glass will be broken into slag in a moment. This is why tempered glass cannot be processed after it is made. Whether you try to drill a hole in it, smash it with a pointed object, or just scratch the surface with a glass knife, you can immediately scrap it.
The degree of glass breakage is closely related to the surface compressive stress formed during the tempering process. The larger the compressive stress, the more completely the glass is broken, and the more secure the fragments it forms. This is very important, because those broken glass doors and windows or bathroom glass, as long as it has sharp angles, can still cause skin scratches, and can even cut blood vessels in severe cases.
In order to make the glass more secure, people not only use heat-treated tempered glass, but also add a polymer film between the two layers of glass, so that even if it is broken by impact, the fragments will not fall down and fly everywhere. Yes. This laminated safety glass is common in cars and it has become standard on windshields.